Engine zinc lesson. - SailNet Community
 
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post #1 of 8 Old 10-26-2008 Thread Starter
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Engine zinc lesson.

I replaced my pencil zinc today and found just the tip and the base eaten away. The base was 80% gone, the mid part of the shaft was almost fully intact. The zinc was at risk of breaking off at the base and falling into the heat exchanger. After some inspection I think the problem was the sticky stuff left over from the price tag protected the shaft of the zinc. The tag had been removed and the stickum could not be seen, but the left over glue was enough to protect it. I sanded the next one down a bit to remove any residue. I have seen cases of people painting or otherwise coating their zincs and making them worthless, but would not have thought left over price tag schmutz would do this.
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post #2 of 8 Old 10-26-2008
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IMHO protecting zincs is a bad thing. If the zinc isn't being eaten something else more important may be.
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post #3 of 8 Old 10-27-2008
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I must admit, I found the post puzzling.

Zincs are supposed to be eaten away.

If they are being eaten away too quickly (and defining "too quickly" is a moving target), then it is safe to assume you have some sort of a galvanic issue, either around or in the boat.

Do you leave your shore power on when absent? Is there known current in the marina/basin?

Without knowing the length of time the zinc spent in the engine and the other particulars, it's hard to know how to absorb this "lesson".
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post #4 of 8 Old 10-27-2008
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I think the issue is the uneven deterioration of the zinc due to where the price tag had been. It sounds like the zinc was going to break off and drop into the cooling water flow and get caught up in the exchanger some place which could be a hassle until the piece completely dissolved. It's always something it seems.

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post #5 of 8 Old 10-27-2008 Thread Starter
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Yes, the point was not that it was going away too fast, but rather was not going away in those parts that were protected. The zinc is changed every 6 months before it is all gone.
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post #6 of 8 Old 10-27-2008
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OK, I understand a little better now.

Is that usual wastage, however? Mine get changed every three or four years.
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post #7 of 8 Old 10-27-2008 Thread Starter
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Like all zinc issues it seems to depend on the boat, if it is in salt water, stray current in the water etc. Since the engine is attached to the shaft which is in the water, I assume an engine zinc might go at a similar rate as external zinc on the hull or shaft itself. I am sure others know more about this than I. On my boat it is about 50% gone in 6 months.
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post #8 of 8 Old 10-28-2008
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Depends a lot on the boat and what mix of metals was used in the cooling system. The greater the mix of metals, the greater the likelihood of galvanic corrosion issues, and the faster the zinc will get eaten.
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OK, I understand a little better now.

Is that usual wastage, however? Mine get changed every three or four years.

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